The Nuclear Energy Agency (NEA) has issued a high priority request list for improved precision of prompt fission gamma measurements. One of the intrinsic difficulties with obtaining precise data of prompt fission quantities is the complete separation of gamma and neutron induced counts in the scintillators. In this work, a new method is proposed for discriminating between the two types of radiation. The data analysis is performed on data sets collected with the STEFF spectrometer, in the 0.1-8 MeV energy range, during two experimental campaigns at the Institut Laue-Langevin (Grenoble) and at the Neutron Time-of-Flight facility at CERN. All the measurements were taken for 235U(nth,f ) reaction. A parametrization was carried out by fitting the gamma time-spectra for each detector with a function composed of a Gaussian, a Watt and a constant distribution, the three corresponding to the gamma, neutron and background components of the spectrum. Neutron contamination was calculated for each spectrum and plotted against energy. A functional form was inferred then fo the variation of neutron contamination with energy by running a simulation of the neutron contribution in Geant IV using the GEF code.